Danke für deine Antwort, aber das Beispiel ist (auch) nicht kompilierbar.
LaTeX Font Info: ... okay on input line 45.
! Undefined control sequence.
\\Preis ... \l_preis_cent_tl {0}}\int_compare:nTF
{\l_preis_euro_tl <=\c_zer...
l.46 \Preis{2}[25]
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.